Substantial amounts of waste cooking oil are obtained worldwide from household and catering enterprises because of deep-frying and other cooking activities. Supercritical water gasification is considered as an aqueous phase reforming process to produce hydrogen enriched syngas from biomass and other organic wastes. In this study, waste cooking oil was gasified at variable temperatures (375-675 degrees C), feed concentration (25-40 wt%) and reaction time (15-60 min) to investigate their effects on syngas yield and composition. Maximum yields of hydrogen (5.16 mol/kg) and total gases (10.5 mol/kg) were obtained at optimal temperature, feed concentration and reaction time of 675 degrees C, 25 wt% and 60 min, respectively. At 5 wt% loading, Ru/Al2O3 enhanced hydrogen yield (10.16 mol/kg) through water-gas shift reaction, whereas Ni/Si-Al2O3 improved methane yield (8.15 mol/kg) via methanation reaction. The trend of hydrogen production from catalytic supercritical water gasification of waste cooking oil at 675 degrees C, 25 wt% and 60 min decreased as Ru/Al2O3 > Ni/Si-Al2O3 > K2CO3 > Na2CO3. The results indicate the recycling potential of waste cooking oil for hydrogen production through hydrothermal gasification. (C) 2018 Elsevier Ltd. All rights reserved.